1. Field of the Invention
The present invention relates to a three terminal capacitor, and more particularly, it relates to a three terminal filter which is suitably applied to a noise filter.
2. Description of the Prior Art
FIG. 9 schematically shows a conventional three terminal capacitor which is disclosed in, e.g., U.S. Pat. No. 4,320,364. Referring to FIG. 9, capacitor electrodes 2 and 3 are provided on front and rear surfaces of a discoidal dielectric substrate 1. A substantially U-shaped hot lead terminal 4 and a ground lead terminal 5 are connected/fixed to each of the electrodes 2 and 3 by solder or the like. Both leg portions 6 and 7 of the hot lead terminal 4 pass through ferrite beads 8 and 9, which are fixed to the leg portions 6 and 7 by an adhesive agent or the like. An armoring member 10 of insulating resin or the like is provided to cover the periphery of the dielectric substrate 1, if necessary.
The conventional three terminal capacitor of the aforementioned structure forms an equivalent circuit as shown in FIG. 3. This capacitor is used as shown in FIG. 10, for example. Referring to FIG. 10, a printed circuit board 14, which is formed on its rear side with a pair of input/output patterns 11 and 12 and a ground pattern 13, is provided with holes (not shown) passing through the respective patterns 11, 12 and 13 from the front side of the printed circuit board 14. These holes are adapted to receive both the leg portions 6 and 7 of the aforementioned hot lead terminal 4 and the ground lead terminal 5. Thus, both the leg portions 6 and 7 of the hot lead terminal 4 and the ground lead terminal 5 are connected/fixed to the respective patterns 11, 12 and 13 by solder or the like.
In such a conventional three terminal capacitor, however, the leg portions 6 and 7 of the hot lead terminal 4 pass through the ferrite beads 8 and 9 below the dielectric substrate 1, whereby the height of the product is increased, leading to an increase in overall size. Further, since the dielectric substrate 1 must be held between the hot lead terminal 4 and the ground lead terminal 5, positioning of the dielectric substrate 1 is difficult. The dielectric substrate 1 may easily be moved during a holding step before soldering of the terminals 4 and 5 to the respective electrodes 2 and 3 of the dielectric substrate 1, whereby the unstable product quality is obtained and reliability is reduced. Further, the ferrite beads 8 and 9, having inner diameters larger than the diameters of the leg portions 6 and 7, are mounted on the leg portions 6 and 7 to be fixed to the same by an adhesive agent or the like, whereby positioning of the ferrite beads 8 and 9 with respect to the leg portions 6 and 7 is difficult. Thus, the ferrite beads 8 and 9 may be irregularly mounted as shown in FIG. 11 for example, whereby the thickness of the product is increased to a level h.sub.1 at the maximum to cause an increase in overall size, while leading to irregular product quality to again reduce reliability. Further, when the capacitor is mounted on the printed circuit board 14 as shown in FIG. 10, the ground lead terminal 5 is increased in length, to generate unwanted inductance in the lengthened portion. Thus, the filter characteristics are deteriorated when the product is applied to use in a noise filter.